Gellable treatment fluids comprising amino group gel-time modifiers

ABSTRACT

Gellable treatment fluids comprising: an aqueous base fluid; a base polymer comprising an acrylamide monomer unit; an organic crosslinking agent comprising a crosslinkable polymer; and a gel-time modifier. The organic crosslinking agent comprising a crosslinkable selected from the group consisting of polyethyleneimine, polyvinylamine, any derivative thereof, any salt thereof, and any combination thereof. The gel-time modifier comprising at least one amino group, any salt thereof, any derivative thereof, or any combination thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 13/171,718, filed on Jun. 29, 2011.

BACKGROUND

The present invention relates to methods and compositions for reducingthe amount of water produced from a subterranean formation, and, morespecifically, to methods and compositions for treating at least aportion of a subterranean formation to reduce water permeability using agellable treatment fluid that comprises a gel-time modifier comprisingat least one amino group.

Water often undesirably accompanies the production of oil and gas from awell penetrating a subterranean formation. The unwanted production ofwater from hydrocarbon-producing wells can constitute a considerabletechnical problem and expense in oilfield operations. If the ratio ofproduced-water to produced-oil and gas becomes sufficiently large, thecost of separating the water and disposing of it can become a barrier tocontinued production. This can lead to abandonment of a well penetratinga subterranean formation, even when significant amounts of hydrocarbonsremain therein.

In a subterranean formation, water's high mobility often allows it toflow to or from a well bore by way of natural and manmade fractures,high permeability zones, and the like. In such cases, less permeablezones in the formation can be bypassed. The bypassing of less permeablezones can be especially problematic when an aqueous treatment fluid isintroduced into a subterranean formation. For example, in enhanced oilrecovery techniques, an aqueous fluid can be introduced into asubterranean formation during water flooding operations. When lesspermeable zones are present in the subterranean formation, lower oil andgas production can occur due to a less effective water floodingoperation being realized. The presence of natural and manmade fractures,high permeability zones and the like also poses problems when aqueousfluids need to be introduced into low permeability zones for purposesother than flooding operations. Examples can include acid stimulationtreatments and near-wellbore cleanup fluids. In such cases, aqueousfluids can preferentially enter high permeability zones and bypass lowpermeability zones, which are the intended targets of fluid treatments.

One way in which the foregoing problems can be addressed is throughconformance control treatments, whereby high permeability zones becomefully or partially blocked to fluid flow. In the case of unwanted waterproduction, full blockage of water producing permeable zones, regardlessof high or low permeability, can stop the unwanted production of water.In the case of flooding operations, partial blocking of highpermeability zones can enable oil production from bypassed lowpermeability zones. In the case of stimulation and near wellborecleanup, partial blocking of high permeability zones can allow diversionof a stimulation fluid (e.g., an acid) or well cleanup fluid to a lowpermeability zone.

Conformance control treatments can involve introducing gellable polymersystems into a subterranean formation via an aqueous treatment fluid.The gellable polymer systems can form a gel through crosslinking awater-soluble polymer using a crosslinking agent. The gel-time and thegel strength of the gellable polymer systems are among the factors thatcan determine the effectiveness of a conformance control treatment. Forexample, if the gel-time is too short, introduction or placement of thegellable polymer system into a subterranean formation can proveproblematic. Conversely, if the gel-time is too long, the gellablepolymer system may not form a gel in the desired portion of thesubterranean formation, or long waiting periods may be required beforefurther operations can be carried out.

A number of crosslinking agents can be used to crosslink water-solublepolymers in gellable polymer systems. Chromium and other transitionmetal ions can be used to crosslink acrylamide-containing polymers andcopolymers. Generally, gels formed using such crosslinking agents haveproven unsuitable at higher temperatures (e.g., above about 80° C.) dueto uncontrolled crosslinking rates (e.g., short gel-times), crosslinkingagent precipitation, polymer degradation, and the like. In addition,chromium and certain other transition metal ions can have an undesirableenvironmental impact. Acrylamide-containing polymers, copolymers, andpartially hydrolyzed variants thereof can also be gelled withpolyalkyleneimines and polyalkylenepolyamines. In such gellable polymersystems, the gel-times are often so short that the crosslinking agentand water-soluble polymer are generally pumped downhole separately inorder to prevent premature gellation from occurring. Gel-timeaccelerators and gel-time retarders have also been used in the art tomodify the gel-times in such systems.

Gellable polymer systems typically comprise a crosslinkable polymer anda crosslinking agent. Normally, as the concentration of either of thesecomponents decreases in a treatment fluid, the time required to form agel as measured by an increase in viscosity of the treatment fluid at agiven temperature, referred to herein as “gel-time,” increases.Typically, the gel-time is determined by measuring the viscosity of atreatment fluid comprising the gellable polymer system as a function oftime. Although treatment fluids having lower concentration gellablepolymer systems are desirable from a cost-of-goods standpoint, increasedgel-times at lower concentrations can make such treatment fluidsineffective for treating a subterranean formation.

The gel-time of a treatment fluid comprising a gellable polymer systemis usually a function of temperature and the concentrations ofwater-soluble polymer and crosslinking agent therein. Generally, athigher concentrations of these components, shorter gel-times can result.Conversely, at lower concentrations, gel-times can be increased. In someinstances, low concentration gellable polymer systems can have gel-timesthat are increased to such an extent that they become ineffective fortreating a subterranean formation. Furthermore, at lower concentrations,the gel strength can also be impacted to some degree. Although gelstrength is not typically a concern in most conformance controltreatment fluids due to relatively high concentrations of water-solublepolymer and crosslinking agent being used, it bears mentioning that gelstrength can be reduced in low concentration gellable polymer systems.

In conformance control treatments using acrylamide-containing polymersand copolymers and crosslinking agents such as, for example,polyethyleneimine and polyalkylenepolyamines, relatively highconcentrations of both components are typically used. From an economicstandpoint alone, it would be desirable to reduce the amounts of eitherof these materials while still maintaining acceptable gel-times andgel-strengths to achieve successful conformance control. Forpolyethyleneimine, in particular, it would also be desirable to reducethe amounts of this highly corrosive material being used in conformancecontrol treatment fluids in order to improve their environmental rating.

SUMMARY OF THE INVENTION

The present invention relates to methods and compositions for reducingthe amount of water produced from a subterranean formation, and, morespecifically, to methods and compositions for treating at least aportion of a subterranean formation to reduce water permeability using agellable treatment fluid that comprises a gel-time modifier comprisingat least one amino group.

In one embodiment, the present invention provides a method comprising:providing a gellable treatment fluid that comprises: an aqueous basefluid; a base polymer comprising an acrylamide monomer unit; an organiccrosslinking agent; and a gel-time modifier comprising at least oneamino group, any salt thereof, any derivative thereof, or anycombination thereof; introducing the gellable treatment fluid into atleast a portion of a subterranean formation; and allowing the gellabletreatment fluid to form a gel in the subterranean formation.

In one embodiment, the present invention provides a method comprising:providing a gellable treatment fluid that comprises: an aqueous basefluid; a base polymer comprising an acrylamide monomer unit; an organiccrosslinking agent comprising a crosslinkable polymer selected from thegroup consisting of polyethyleneimine, polyvinylamine, any derivativethereof, any salt thereof, and any combination thereof; and a gel-timemodifier comprising at least one compound selected from the groupconsisting of amino alcohols, oligomeric polyamines, any salt thereof,any derivative thereof, and any combination thereof; and wherein thegellable treatment fluid has a reduced gel-time relative to a likegellable treatment fluid lacking the gel-time modifier; introducing thegellable treatment fluid into at least a portion of a subterraneanformation; and allowing the gellable treatment fluid to form a gel inthe subterranean formation.

In one embodiment, the present invention provides a gellable treatmentfluid comprising: an aqueous base fluid; a base polymer comprising anacrylamide monomer unit; an organic crosslinking agent comprising acrosslinkable polymer selected from the group consisting ofpolyethyleneimine, polyvinylamine, any derivative thereof, any saltthereof, and any combination thereof; and a gel-time modifier comprisingat least one amino group, any salt thereof, any derivative thereof, orany combination thereof.

The features and advantages of the present invention will be readilyapparent to one of ordinary skill in the art upon a reading of thedescription of the preferred embodiments that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of thepresent invention, and should not be viewed as exclusive embodiments.The subject matter disclosed is capable of considerable modification,alteration, and equivalents in form and function, as will be evident toone having ordinary skill in the art and the benefit of this disclosure.

FIG. 1 shows an illustrative plot of viscosity as a function of time at160° F. for various gellable treatment fluids comprising at-butylacrylate/acrylamide base polymer, polyethyleneimine, and,optionally, an amino alcohol gel-time modifier.

FIG. 2 shows an illustrative plot of viscosity as a function of time at160° F. for various gellable treatment fluids comprising at-butylacrylate/acrylamide base polymer, polyethyleneimine, and,optionally, a diethylenetriamine gel-time modifier.

FIG. 3 shows an illustrative plot of viscosity as a function of time at160° F. for various gellable treatment fluids comprising at-butylacrylate/acrylamide base polymer, polyethyleneimine, and,optionally, a triethylenetetraamine gel-time modifier.

FIG. 4 shows an illustrative plot of viscosity as a function of time at160° F. for various gellable treatment fluids comprising at-butylacrylate/acrylamide base polymer, polyethyleneimine, and,optionally, an amino alcohol gel-time modifier.

FIG. 5 shows an illustrative plot of viscosity as a function of time at160° F. for various gellable treatment fluids comprising at-butylacrylate/acrylamide base polymer, polyethyleneimine, and,optionally, an amino alcohol gel-time modifier.

FIG. 6 shows an illustrative plot of viscosity as a function of time at250° F. for various gellable treatment fluids comprising at-butylacrylate/acrylamide base polymer, polyethyleneimine, and,optionally, an amino alcohol gel-time modifier.

FIG. 7 shows an illustrative plot of viscosity at 160° F. as a functionof time for various gellable treatment fluids comprising at-butylacrylate/acrylamide base polymer, polyethyleneimine,tetramethylammonium chloride, and, optionally, ethanolamine.

FIG. 8 shows an illustrative plot of viscosity at 160° F. as a functionof time for various gellable treatment fluids comprising a partiallyhydrolyzed polyacrylamide, polyethyleneimine and various gel modifiersin a 2% KCl base fluid.

FIG. 9 shows an illustrative plot of viscosity at 160° F. as a functionof time for various gellable treatment fluids comprising a partiallyhydrolyzed polyacrylamide, polyethyleneimine and various gel modifiersin a 7% KCl base fluid.

DETAILED DESCRIPTION

The present invention relates to methods and compositions for reducingthe amount of water produced from a subterranean formation, and, morespecifically, to methods and compositions for treating at least aportion of a subterranean formation to reduce water permeability using agellable treatment fluid that comprises a gel-time modifier comprisingat least one amino group.

There are many advantages of the present invention. For instance, thepresent invention provides treatment fluid compositions and methods foruse thereof in which gellable polymer systems are present in lowerconcentrations than are conventionally used in the art, while stillproviding gel-times that are of an effective length for suitabledownhole placement and performance to be realized. As defined herein, a“treatment fluid” is a fluid that is placed in a subterranean formationin order to perform a desired function. Treatment fluids can be used ina variety of subterranean operations, including, but not limited to,drilling operations, production treatments, stimulation treatments,remedial treatments, fluid diversion operations, fracturing operations,secondary or tertiary EOR operations, and the like. As used herein, theterms “treatment” and “treating” refer to any subterranean operationthat uses a fluid in conjunction with performing a desired functionand/or achieving a desired purpose. The terms “treatment” and“treating,” as used herein, do not imply any particular action by thefluid or any particular component thereof unless otherwise specified.Treatment fluids can include, for example, drilling fluids, fracturingfluids, acidizing fluids, conformance treatment fluids, damage controlfluids, remediation fluids, scale removal and inhibition fluids,chemical floods, and the like.

According to the present embodiments, it has been surprisinglydiscovered that inclusion of the present gel-time modifiers can reducethe gel-time in a treatment fluid comprising a gellable polymer system.In the case of a low concentration gellable polymer system, theadditives can reduce the gel-time to a level that is more amenable fortreating a subterranean formation. That is, the additives can serve asgel-time promoters in such embodiments. However, in some alternativeembodiments, the additives can increase the gel-time at higher additiveconcentrations. That is, the additives can serve as gel-time retardersin these embodiments. In such embodiments, the additives can increasethe gel-time of a treatment fluid whose gel-time is otherwise too shortto be useful for a desired application. Hence, the present additives canbe added to a treatment fluid comprising a gellable polymer system insufficient amounts to increase or to decrease the gel-time to a desiredextent.

More specifically, it has been surprisingly discovered that treatmentfluids comprising a base polymer comprising an acrylamide monomer unit(e.g., polyacrylamide, acrylamide copolymers, and partially hydrolyzedversions thereof) and an organic crosslinking agent (e.g.,polyethyleneimine and polyalkyleneamines), can have reduced gel-timeswhen small amounts of a gel-time modifier that comprises at least oneamino group are included in the treatment fluid. Illustrative compoundscomprising at least one amino group that can modify the gel-timesaccording to the present embodiments include, for example, aminoalcohols and oligomeric polyamines (e.g., diethylenetriamine,triethylenetetraamine, and tetraethylenepentaamine). Although polyaminecompounds having much higher molecular weights (e.g., polyethyleneimineand polyalkyleneamines), can induce crosslinking of acrylamide polymers,it has been found in control experiments that amino alcohols and smallmolecule oligomeric polyamines do not appear to effectively crosslink(or even initiate measurable crosslinking) with acrylamide polymersalone. Hence, the fact that amino alcohols and oligomeric polyamines canfacilitate crosslinking is particularly surprising. Further, the factthat the amino alcohols and oligomeric polyamines become gel-timeretarders at higher concentration is also surprising, since it wouldordinarily be expected that gel-time promotion would continuallyincrease with increasing concentration.

Other additives can also be used in combination with the gel-timemodifiers comprising at least one amino group, as discussed hereinafter,to further modify the gel-times. For example, in one embodiment,quaternary ammonium salts can be used to further modify the gel-times.

Concerns have recently been raised regarding the environmental impact oftreatment fluids used for various subterranean operations. Since thetreatment fluids of the present invention can comprise a lowerconcentration of at least one of the components of the gellable polymersystem than do conventional treatment fluids having comparablegel-times, the present treatment fluids can be particularly advantageousfrom an environmental standpoint. Particularly, in some embodiments, thepresent treatment fluids can comprise a lower concentration ofcrosslinking agent and/or base polymer than would otherwise be requiredto achieve a given gel-time. In more specific embodiments, use of agel-time modifier comprising at least one amino group in the presenttreatment fluids can allow lower concentrations of polyethyleneimine,which is highly corrosive, to be used in the treatment fluid.

In some applications, depending on the subterranean formation, inorganicsalts (e.g., alkali metal salts or alkaline earth metal salts), such assodium chloride or potassium chloride can be included in treatmentfluid. Generally, an increase in salt concentration can increase thegel-time. The increase in gel-time can be particularly problematic atlow temperatures, where gel-times are inherently longer because ofslower chemical reaction rates at low temperatures. Increased gel timesin treatment fluids comprising a salt can be advantageously compensatedfor, in some embodiments, by using gel-time accelerators. At hightemperatures, gel-times are shorter. By selecting an appropriateconcentration of a gel-time modifier, use of the treatment fluids athigher temperatures can become possible. Specifically, in someembodiments, the gel-time modifiers can increase the gel-time such thatan appropriate gellation rate can be realized under high temperatures.

Although the present disclosure primarily describes treatment fluidsthat can be used in conformance control operations, it is to beunderstood that the treatment fluids of the present invention can beused in any of the drilling stage, the production stage, the stimulationstage, enhanced oil recovery (EOR) operations, or the remediation stageof a subterranean operation. Any of these operations can benefit fromthe reduced amount of water produced from the subterranean formation orfrom decreased formation water permeability, for example.

Treatment fluids of the present invention generally comprise an aqueousbase fluid as the continuous phase. Aqueous phase base fluids caninclude, for example, fresh water, acidified water, salt water,seawater, brine, or an aqueous salt solution. In some embodiments, thetreatment fluids can also comprise small amounts of hydrocarbons suchthat the aqueous base fluid remains as the continuous phase. The smallamounts of hydrocarbons can be introduced from any source. In oneembodiment, introduction of small amounts of hydrocarbons in the presenttreatment fluids can take place concurrently with the components of thegellable polymer system, as some of these components may be obtainedcommercially in a hydrocarbon base fluid. It is not believed that smallamounts of hydrocarbons, when present, significantly impact thetreatment fluid's performance in forming a gel.

In various embodiments, treatment fluids of the present invention caninclude an aqueous base fluid as the continuous phase. In someembodiments, the aqueous base fluid can be an aqueous salt solution.Such aqueous salt solutions can have a salt concentration rangingbetween about 0.1% and about 10% by weight. The salt concentration canrange between about 1% and about 10% by weight in some embodiments orbetween about 2% and about 5% by weight in other embodiments. In certainembodiments, some or all of the salt can be replaced by anothermaterial. For example, in some of the present embodiments, the gel-timemodifier comprising at least one amino group can replace at least aportion of the salt in the aqueous base fluid. That is, such treatmentfluids can have a lower salt concentration than a like treatment fluidlacking the gel-time modifier. In other embodiments, the gel-timemodifier can be used in a base fluid that is comparable in compositionto a like treatment fluid lacking the gel-time modifier. That is, insuch embodiments, the gel-time modifier does not replace the salt of thebase fluid. The salt of the aqueous salt solution is generally an alkalimetal or alkaline earth metal salt. Of these, sodium chloride andpotassium chloride are presently preferred. Other alkali metal oralkaline earth metal salts such as, for example, nitrates, acetates, andsoluble formates can also be used for forming the aqueous salt solution.

In some embodiments, gellable treatment fluids of the present inventioncan comprise an aqueous base fluid, a base polymer that comprises anacrylamide monomer unit, an organic crosslinking agent, and a gel-timemodifier that comprises at least one amino group.

In some embodiments, the gellable treatment fluids can have a reducedgel-time relative to that of a like treatment fluid lacking the gel-timemodifier. In alternative embodiments, the gellable treatment fluids canhave an increased gel-time relative to that of a like treatment fluidlacking the gel-time modifier. Increased gel-times are typicallyobserved at higher concentration of the gel-time modifier. As usedherein, the term “like treatment fluid” refers to a second treatmentfluid having substantially the same composition as that of a firsttreatment fluid, with the exceptions of: 1) the second treatment fluidhaving a different concentration of at least one component, and 2) thesecond treatment fluid lacking the gel-time modifier comprising aquaternary ammonium salt. Inert components that do not substantiallyaffect the gel-time can also be present in a “like treatment fluid.”

In some embodiments, the base polymers can be water soluble. In someembodiments, the base polymers of the present treatment fluids cancomprise an acrylamide monomer unit. Such base polymers can include, forexample, polyacrylamide, acrylamide copolymers, and partially hydrolyzedversions thereof. In alternative embodiments, base polymers thatcomprise a methacrylamide monomer unit can be used. Examples of suitable(meth)acrylamide base polymers are described in U.S. Pat. No. 6,176,315which is incorporated herein by reference in its entirety. Such basepolymers can include, for example, water soluble polymethacrylamide,methacrylamide copolymers, and partially hydrolyzed variants thereof.Optionally, acrylamide and methacrylamide monomers can be used incombination with one another. In some embodiments, the base polymer canbe a partially hydrolyzed polyacrylamide. Such a base polymer isavailable from Halliburton Energy Services of Duncan, Okla. under thetradename “FDP-835™,” which has a molecular weight of about 640,000. Insome embodiments, the base polymer can be a copolymer of acrylamide andan acrylate. In more specific embodiments, the base polymer can be acopolymer of acrylamide and t-butyl acrylate. Such a base polymer isavailable from Halliburton Energy Services of Duncan, Okla. under thetradename “HZ-10™,” which has a molecular weight of about 107,000. Instill other embodiments, the base polymer can be a copolymer ofacrylamide and/or methacrylamide and monomers such as, for example,ethylene, propylene, styrene, maleic anhydride, and the like. Suchpolymers can also be partially hydrolyzed. In still other alternativeembodiments, an acrylate ester monomer unit can replace acrylamide ormethacrylamide or be used in combination with acrylamide ormethacrylamide.

A portion of a base polymer comprising an acrylamide monomer unit isshown in Formula (1) below, where the wavy lines represent bonding toother monomer units.

In some embodiments, the base polymer can comprise an acrylate estermonomer unit. A portion of a base polymer comprising an acrylate estermonomer unit is shown in Formula (2) below, where the wavy linesrepresent bonding to other monomer units and R is an alkyl or arylgroup, for example.

In some embodiments, base polymers comprising acrylamide or acrylateester monomer units can be at least partially hydrolyzed. As usedherein, the term “at least partially hydrolyzed” refers to base polymersthat have at least a portion of their side chain amide or ester groupshydrolyzed to form side chain acid groups. That is, base polymers thatare partially hydrolyzed have at least some acrylic acid monomer units.In various embodiments, the degree of hydrolysis can range from about0.1% to about 30% of the acrylamide/acrylate monomer units. A partialstructure of a base polymer comprising acrylic acid monomer units isshown in Formula (3) below, where the wavy lines represent bonding toother monomer units (e.g., other acrylic acid monomer units and/or otheracrylamide or acrylate ester monomer units).

Depending on the pH of the treatment fluid, base polymers that are atleast partially hydrolyzed can have their acidic side chains protonated(i.e., acidic) or deprotonated (i.e., anionic form). In variousembodiments, the base polymers of the present invention can have amolecular weight ranging between about 100,000 and about 20,000,000.

Among other factors, the performance of the preceding base polymers canbe impacted by the temperature at which they are allowed to gel. Thatis, the gel-times of the base polymers can vary depending on thetemperature of the subterranean formation to which they are introduced.For example, a base polymer that produces an acceptable gel-time atlower temperatures can gel at an unacceptably fast rate at highertemperatures. Conversely, a base polymer that gels at an acceptable rateat higher temperature may not gel at an acceptable rate, if at all, atlower temperatures. For conformance control treatments using thespecific base polymers set forth above in combination withpolyethyleneimine as an organic crosslinking agent, anacrylamide/t-butyl acrylate copolymer is typically used when thetemperature of the subterranean formation is about 160° F. or higher,whereas a partially hydrolyzed polyacrylamide is typically used when thesubterranean formation has a temperature ranging between about 60° F.and about 160° F. It is to be noted that these preferred operatingtemperature ranges are for gellable treatment fluids that lack agel-time modifier comprising at least one amino group or any othergel-time modifier. Use of a gel-time modifier as in the presentembodiments can allow an expanded effective operating temperature rangeof the base polymer. Accordingly, the present treatment fluids can beeffectively used at temperatures lower than those conventionally used inthe art, particularly those treatment fluids that comprise anacrylamide/t-butyl acrylate copolymer.

In some embodiments, the base polymers of the present invention are nothydrophobically modified. As used herein, the term “not hydrophobicallymodified” refers to a base polymer that does not comprise a hydrophobicmodification thereon. As used herein, a hydrophobic modification of abase polymer will be considered to be any hydrophobic group having morethan about 4 carbon atoms. More particularly, in some embodiments, thebase polymers of the present invention lack monomer units having aquaternized nitrogen atom and a hydrophobic modification thereon.

Particularly suitable organic crosslinking agents that can be used withthe above base polymers are themselves crosslinkable polymers. In someembodiments, suitable crosslinkable polymers include, for example,polyalkyleneimines and polyalkylenepolyamines, any derivative thereof,any salt thereof, and any combination thereof. In more specificembodiments, suitable crosslinkable polymers include, for example,polyethyleneimine, polyvinylamine (polyethylenepolyamine), anyderivative thereof, any salt thereof, and any combination thereof. Inalternative embodiments, suitable crosslinkable polymers can includepolypropyleneimine, polypropylenepolyamine, polyallylamine, anyderivative thereof, any salt thereof, and any combination thereof. Inyet other alternative embodiments, the organic crosslinking agent can bechitosan, polymyxins, polylysine, any derivative thereof, any saltthereof, and any combination thereof.

In some embodiments, suitable gel-time modifiers that comprise at leastone amino group can be amino alcohols, oligomeric polyamines, any saltthereof, any derivative thereof, or any combination thereof. In general,it is contemplated that any amine compound that has at least somemiscibility with water can be suitable for use in the presentembodiments. It is also contemplated that any derivative of aminoalcohols or oligomeric polyamines comprising derivatized amino nitrogenatoms can undergo reactions under downhole conditions to release theamino groups in underivatized form. That is, precursors to such aminoalcohols and oligomeric polyamines are also contemplated by the presentembodiments. For example, it is contemplated that amine compoundscomprising an acylated amino group can undergo hydrolysis under downholeconditions to release free amino groups, which then function as gel-timemodifiers.

Illustrative amino alcohol gel-time modifiers can include, for example,ethanolamine, diethanolamine, triethanolamine, propanolamine,triisopropanolamine, any salt thereof, any derivative thereof, anycombination thereof, and the like. When present in a salt form, the freeamino alcohol can be regenerated either by pH adjustment prior topumping downhole in some embodiments or under suitable downholeconditions in other embodiments.

Oligomeric polyamines suitable for use in the present embodimentsgenerally have a molecular weight of less than about 400. That is, theoligomeric polyamines suitable for use in the present embodiments arenon-polymeric amine compounds. Illustrative examples of suitableoligomeric polyamines can include, for example, diethylenetriamine,triethylenetetraamine, tetraethylenepentaamine, any salt thereof, anyderivative thereof, any combination thereof, and the like. When presentin a salt form, the free oligomeric polyamine can be regenerated eitherby pH adjustment prior to pumping downhole in some embodiments or undersuitable downhole conditions in some embodiments. In alternativeembodiments, non-oligomeric amines such as, for example, propylamine,butylamine, diethylamine, diisopropylamine, ethyldiisopropylamine,trimethylamine, triethylamine, pyridine, and the like can be used.

In general, the gel-times of the present treatment fluids are a functionof the amount of gel-time modifier used. Generally, higherconcentrations of the gel-time modifier comprising at least one aminogroup can lead to shorter gel-times. However, above a thresholdconcentration of the gel-time modifier, longer gel-times can result.Hence, according to some embodiments of the present invention, agel-time modifier comprising at least one amino group can be added to atreatment fluid comprising a gellable polymer system of a givencomposition in order to increase or decrease the gel-time.

Without being limited by theory, it is believed that the mechanism bywhich an amine-containing gel-time modifier functions as a gel-timeaccelerator or a gel-time retarder can be explained as follows.Crosslinking agents such as, for example, polyethyleneimine andpolyalkylene polyamines can exist in partially protonated forms inaqueous fluids. The degree of protonation can depend on the pH of thefluid, the type of amino group (e.g., primary, secondary or tertiary,aliphatic or aryl amino groups) and the polymer structure. It isbelieved that a crosslinking agent comprising protonated amino groupsdoes not function as a crosslinking center due to the unavailability ofthe lone pair electrons on the nitrogen atom. It is further believedthat amine-containing gel-time modifiers can deprotonate protonatedamino nitrogen atoms in the crosslinking agent, thus making themavailable for crosslinking reactions and reducing the gel-time. Athigher concentrations of gel-time modifier, it is believed that therecan be an excess of amino groups from the gel-time modifier, even afterdeprotonating the amino nitrogen atoms in crosslinking agent. It isbelieved that the excess amino groups can react with water to generatehydroxide ions according to Equation (1), where R is an alkyl or arylgroup.R—NH₂+H₂O→R—NH₃ ⁺+OH⁻  (1)It is believed that the generated hydroxide ion can hydrolyze amidefunctional groups in the crosslinking agent to generate carboxylate ionsaccording to Equation (2).OH⁻+R—C(O)NH₂→R—C(O)O⁻+NH₃  (2)It is generally the case that increased hydrolysis levels inpolyacrylamide polymers can increase gel-times of a treatment fluidformed therefrom.

Generally, the base polymer, the organic crosslinking agent, and thegel-time modifier are used together in concentrations that areappropriate to achieve a desired gel-time for a given application. Giventhe benefit of the present disclosure, one of ordinary skill in the artwill be able to determine appropriate concentrations of the basepolymer, the organic crosslinking agent, and the gel-time modifierthrough routine experimentation. In some embodiments, the gellabletreatment fluids of the present invention can have reduced gel-timesrelative to a like gellable treatment fluid that lacks the gel-timemodifier.

In some embodiments, the concentration of the gel-time modifier can beless than about 5% by weight. In other embodiments, the concentration ofthe gel-time modifier can be less than about 2% by weight. In stillother embodiments, the concentration of the gel-time modifier can beless than about 1% by weight. In some embodiments, the concentration ofthe gel-time modifier can range between about 0.1% and about 1% byweight. In some embodiments, the concentration of the gel-time modifiercan range between about 0.2% and about 0.8% by weight. In still otherembodiments, the concentration of the gel-time modifier can rangebetween about 1% and about 2% by weight.

Generally, the concentration of the base polymer can be about 10% orless by weight in a treatment fluid lacking the gel-time modifiercomprising at least one amino group. Likewise, the concentration of theorganic crosslinking agent can be typically about 5% or less by weightin a treatment fluid lacking the gel-time modifier comprising at leastone amino group. In treatment fluids of the present invention, theconcentrations of the base polymer and the organic crosslinking agentcan generally be at the foregoing values or lower. In some embodiments,inclusion of a gel-time modifier comprising at least one amino group canallow the concentration of at least one of the base polymer or theorganic crosslinking agent to be reduced by at least about 20% relativeto a like treatment fluid lacking the gel-time modifier, whilemaintaining a gel-time that is suitable for use in a subterraneanformation. In other embodiments inclusion of the gel-time modifiercomprising at least one amino group can allow the concentration of atleast one of the base polymer or the organic crosslinking agent to bereduced by at least about 40% relative to a like treatment fluid lackingthe gel-time modifier. In still other embodiments inclusion of thegel-time modifier comprising at least one amino group can allow theconcentration of at least one of the base polymer or the organiccrosslinking agent to be reduced by at least about 60% relative to alike treatment fluid lacking the gel-time modifier. In some embodiments,at lower concentrations of the base polymer and/or the organiccrosslinking agent, the gel-time can be substantially the same as thatof a like treatment fluid of higher concentration lacking the gel-timemodifier. In other embodiments, the gel-time can be intermediate betweenthat of a like treatment fluid of higher concentration lacking thegel-time modifier and a like treatment fluid of lower concentrationlacking the gel-time modifier. Thus, it is not a necessary conditionthat the treatment fluids of the present invention have a gel-time thatis substantially the same as that of higher concentration treatmentfluid. According to the present embodiments, the present treatmentfluids have a gel-time that is altered from that of a like treatmentfluid lacking the gel-time modifier. Modification of the gel-time canmake the treatment fluids of the present invention suitable for use in agiven subterranean application.

In some embodiments, the base polymer and the organic crosslinking agentcan be present at a ratio of up to about 50:1 base polymer:organiccrosslinking agent. In other embodiments, the ratio of basepolymer:organic crosslinking agent can be at most about 20:1. In stillother embodiments, the ratio of base polymer:organic crosslinking agentcan be at most about 10:1. In some embodiments, the ratio of basepolymer:organic crosslinking agent can be at least about 5:1. As will beevident to one having ordinary skill in the art, when the amount of basepolymer is reduced in the present treatment fluids with the amount oforganic crosslinking agent remaining the same as a like treatment fluidlacking the gel-time modifier, the ratio of these two components will belower than that of a like treatment fluid of higher concentrationlacking the gel-time modifier. Likewise, when the amount of organiccrosslinking agent is reduced in the present treatment fluids with theamount of base polymer remaining the same as in a like treatment fluidlacking the gel-time modifier, the ratio of the two components will behigher. When the amount of both the base polymer and the organiccrosslinking agent are lowered, the ratio of these two components can belower, higher or the same, depending upon how much the quantity of eachcomponent is lowered relative to the other.

In some embodiments, the present treatment fluids can further compriseat least one additional gel-time modifier in supplement to the gel-timemodifier comprising at least one amino group. Such additional gel-timemodifiers can be gel-time accelerators in some embodiments or gel-timeretarders in other embodiments, depending on whether one wants toincrease or decrease the gel-time in a particular treatment fluid.Illustrative gel-time modifiers can include, for example, pH modifyingagents such as, for example, inorganic acids, organic acids, organicsalts, and inorganic salts. Examples of such gel-time modifiers are setforth in U.S. Pat. Nos. 7,331,390, 7,325,613, 7,322,414, and 7,287,587,and co-pending U.S. patent application Ser. Nos. 12/716,951, 12/716,979and 12/717,004, all filed on Mar. 3, 2010. Specific illustrativeexamples of pH modifying agents can include, for example, alkali metalcarbonates, bicarbonates, acetates, formates, and hydroxides; organicacids (e.g., phenols or acetic acid); mineral acids (e.g., hydrochloricacid); and Lewis acids (e.g., boric acid). Illustrative gel-timeretarders that can be used in the present embodiments include, forexample, transition metal salts that can coordinate the organiccrosslinking agent and acid anhydrides that can at least partiallyacylate amino groups in the organic crosslinking agent. A suitablecoordinated organic crosslinking agent is described in commonly ownedU.S. Pat. No. 6,196,317, which is incorporated herein by reference inits entirety. The use of acid anhydrides as a gel-time retarder isdescribed in commonly owned U.S. Pat. No. 7,091,160, which isincorporated herein by reference in its entirety. When a gel-timeretarder is used, the coordination bond strength or the degree ofacylation can help control the gel-time.

In some embodiments, the at least one additional gel-time modifier canbe compounds other than those described above that have beenconventionally used in the art. For example, in some embodiments, the atleast one additional gel-time modifier can be a quaternary ammoniumsalt. Use of the quaternary ammonium salts as gel-time modifiers isdescribed in commonly owned U.S. patent application Ser. No. 13/171,677,filed on Jun. 29, 2011 concurrently herewith and now available as U.S.Patent Application Publication 2013/0000911, which is incorporatedherein by reference in its entirety. In some embodiments, use of aquaternary ammonium salt in combination with a gel-time modifiercomprising at least one amino group can result in further decreases ingel-time of a gellable polymer system.

Suitable quaternary ammonium salts that can be used in the presenttreatment fluids are typically tetraalkylammonium salts. Illustrativetetraalkylammonium salts can include, without limitation,tetramethylammonium halides, tetraethylammonium halides,tetrapropylammonium halides, tetrabutylammonium halides, and the like.The alkyl groups in the quaternary ammonium salts can be either straightchain or branched. In some embodiments, the treatment fluids of thepresent invention can comprise tetramethylammonium chloride as thequaternary ammonium salt. Longer chain (e.g., >C₄) quaternary ammoniumsalts can be cationic surfactants. However, without being bound bytheory or mechanism of action, it is believed that the quaternaryammonium salts are not functioning in a surfactant role in the presentembodiments. Although it is believed that quaternary ammonium saltshaving any carbon chain length can be used in the present embodiments,it is preferred that the quaternary ammonium salts comprise alkyl groupsin which none of the alkyl groups are larger than C₄ alkyl groups. Inalternative embodiments, however, quaternary ammonium salts that have atleast one alkyl group that is larger than a C₄ alkyl group can also beused. It is to be noted that it is particularly surprising thatquaternary ammonium salts can serve to reduce the gel-times in thepresent treatment fluids, since inorganic ammonium salts have been foundin the art to increase gel-times in like treatment fluids.

In some embodiments, treatment fluids of the present invention canfurther comprise at least one surfactant. Such surfactants includecationic surfactants, anionic surfactants, zwitterionic surfactants, andnon-ionic surfactants, numerous examples of each of which are known toone having ordinary skill in the art. When present, a surfactant can beused in the present treatment fluids at a concentration ranging betweenabout 0.1% and about 2.0% by weight or between about 0.5% and about 1.0%by weight in various embodiments.

Illustrative examples of surfactants can include, without limitation,ethoxylated nonyl phenol phosphate esters, alkyl phosphonates, linearalcohols, nonylphenol compounds, alkoxylated fatty acids, alkylphenolalkoxylates, ethoxylated amides, ethoxylated alkyl amines, betaines,methyl ester sulfonates (e.g., as described in commonly owned U.S. Pat.Nos. 7,159,659; 7,299,874; and 7,303,019 and U.S. patent applicationSer. No. 11/058,611, filed Feb. 2, 2005 (now available as United StatesPatent Application Publication 2006/0183646), the entire disclosures ofwhich are incorporated herein by reference), hydrolyzed keratin (e.g.,as described in commonly owned U.S. Pat. No. 6,547,871, the entiredisclosure of which is incorporated herein by reference),sulfosuccinates, taurates, amine oxides, alkoxylated fatty acids,alkoxylated alcohols (e.g., lauryl alcohol ethoxylate, ethoxylated nonylphenol), ethoxylated fatty amines, ethoxylated alkyl amines (e.g.,cocoalkylamine ethoxylate), modified betaines, alkylamidobetaines (e.g.,cocoamidopropyl betaine) and quaternary ammonium compounds (e.g.,trimethyltallowammonium chloride, trimethylcocoammonium chloride).Suitable surfactants can be used in a liquid or powder form.

Further, the present treatment fluids can optionally comprise any numberof additional additives commonly used in treatment fluids including, forexample, anti-oxidants, polymer degradation prevention additives,relative permeability modifiers, scale inhibitors, corrosion inhibitors,foaming agents, defoaming agents, antifoam agents, emulsifying agents,de-emulsifying agents, iron control agents, proppants or otherparticulates, particulate diverters, salts, acids, fluid loss controladditives, gas, catalysts, clay control agents, dispersants,flocculants, scavengers (e.g., H₂S scavengers, CO₂ scavengers or O₂scavengers), lubricants, breakers, friction reducers, bridging agents,viscosifiers, weighting agents, solubilizers, pH control agents (e.g.,buffers), hydrate inhibitors, consolidating agents, bactericides, andthe like. Combinations of these additives can be used as well.

In some embodiments, the gellable treatment fluids described herein canbe used for treating at least a portion of a subterranean formation. Insome embodiments, such treatments can involve reducing an amount ofwater produced from the portion of the subterranean formation. In someembodiments, such treatments can result in partial or complete reductionin permeability of the subterranean formation to water.

In some embodiments, methods of the present invention can compriseproviding a gellable treatment fluid that comprises an aqueous basefluid, a base polymer that comprises an acrylamide monomer unit, anorganic crosslinking agent, and a gel-time modifier that comprises atleast one amino group, any salt thereof, any derivative thereof, or anycombination thereof; introducing the gellable treatment fluid into atleast a portion of a subterranean formation, and allowing the gellabletreatment fluid to form a gel in the subterranean formation.

In some embodiments, methods of the present invention can compriseproviding a gellable treatment fluid that comprises an aqueous basefluid, a base polymer comprising an acrylamide monomer unit, an organiccrosslinking agent comprising a crosslinkable polymer selected frompolyethyleneimine, polyvinylamine, any derivative thereof, any saltthereof, and any combination thereof, and a gel-time modifier thatcomprises at least one compound selected from amino alcohols, oligomericpolyamines, any salt thereof, any derivative thereof, and anycombination thereof; introducing the gellable treatment fluid into atleast a portion of a subterranean formation; and allowing the gellabletreatment fluid to form a gel in the subterranean formation. In suchembodiments, the gellable treatment fluid can have a reduced gel-timerelative to a like gellable treatment fluid lacking the gel-timemodifier.

To facilitate a better understanding of the present invention, thefollowing examples of preferred embodiments are given. In no way shouldthe following examples be read to limit, or to define, the scope of theinvention.

EXAMPLES Example 1 Gel-Times at 160° F. in Gellable Treatment FluidsComprising a t-Butylacrylate/Acrylamide Base Polymer, Polyethyleneimine,and an Amino Group-Containing Gel-Time Modifier (Reduction ofCrosslinkable Polymer Amounts)

Control gellable treatment fluids were prepared at the followingcompositions: (1) 350 gal/Mgal “HZ-10” and 60 gal/Mgal “HZ-20” in 2%aqueous KCl base fluid, and (2) 350 gal/Mgal “HZ-10” and 30 gal/Mgal“HZ-20” in 2% aqueous KCl base fluid. Inventive treatment fluids wereprepared at the following compositions: (3) 350 gal/Mgal “HZ-10,” 30gal/Mgal “HZ-20,” and 0.36% by weight ethanolamine in 2% aqueous KClbase fluid, (4) 350 gal/Mgal “HZ-10,” 30 gal/Mgal “HZ-20,” and 0.75% byweight ethanolamine in 2% aqueous KCl base fluid, (5) 350 gal/Mgal“HZ-10,” 30 gal/Mgal “HZ-20,” and 0.8% by weight diethanolamine in 2%aqueous KCl base fluid, (6) 350 gal/Mgal “HZ-10,” 30 gal/Mgal “HZ-20,”and 0.36% by weight diethylene triamine in 2% aqueous KCl base fluid,(7) 350 gal/Mgal “HZ-10,” 30 gal/Mgal “HZ-20,” and 0.75% by weightdiethylene triamine in 2% aqueous KCl base fluid, (8) 350 gal/Mgal“HZ-10,” 30 gal/Mgal “HZ-20,” and 1.5% by weight diethylenetriamine in2% aqueous KCl base fluid, (9) 350 gal/Mgal “HZ-10,” 30 gal/Mgal“HZ-20,” and 0.36% by weight triethylenetetraamine in 2% aqueous KClbase fluid, (10) 350 gal/Mgal “HZ-10,” 30 gal/Mgal “HZ-20,” and 0.75% byweight triethylenetetraamine in 2% aqueous KCl base fluid, and (11) 350gal/Mgal “HZ-10,” 30 gal/Mgal “HZ-20,” and 1.5% by weighttriethylenetetraamine in 2% aqueous KCl base fluid. “HZ-10” is at-butylacrylate/acrylamide copolymer that is available from HalliburtonEnergy Services of Duncan, Okla. “HZ-20” is a polyethyleneimine polymerthat is available from Halliburton Energy Services of Duncan, Okla.

The viscosities of the above treatment fluids were measured as afunction of time in order to determine their gel-times. Viscositymeasurements were made at 160° F. FIG. 1 shows an illustrative plot ofviscosity as a function of time at 160° F. for various gellabletreatment fluids comprising a t-butylacrylate/acrylamide base polymer,polyethyleneimine, and, optionally, an amino alcohol gel-time modifier.As shown in FIG. 1, control treatment fluid (1) had a gel-time ofapproximately 350 minutes. When the polyethyleneimine concentration washalved in control treatment fluid (2), the gel-time increased toapproximately 750 minutes. In contrast, when the 0.36 wt. % ethanolaminewas included in inventive treatment fluid (3), the gel-time decreased toabout 600 minutes. A further decrease in gel-time to about 500 minuteswas observed in inventive treatment (4) when the ethanolamineconcentration was doubled to 0.75 wt. %. A similar gel-time was observedin inventive treatment fluid (5), which comprised 0.8 wt. %diethanolamine. Although the gel-times of the inventive treatment fluidsdid not reach those of the original control treatment fluid (1), thegel-times were still significantly reduced compared to that seen forcontrol treatment fluid (2). In the case of inventive treatment fluids(3)-(5), the gel-times were comparable to those obtained when about45-50 gal/Mgal of polyethyleneimine was used in the treatment fluidwithout the amino alcohol gel-time modifier being present.

Similar results were observed when the amino alcohol gel-time modifierwas replaced with an oligomeric polyamine gel-time modifier. FIG. 2shows an illustrative plot of viscosity as a function of time at 160° F.for various gellable treatment fluids comprising at-butylacrylate/acrylamide base polymer, polyethyleneimine, and,optionally, a diethylenetriamine gel-time modifier. FIG. 3 shows anillustrative plot of viscosity as a function of time at 160° F. forvarious gellable treatment fluids comprising at-butylacrylate/acrylamide base polymer, polyethyleneimine, and,optionally, a triethylenetetraamine gel-time modifier. As shown in FIG.2, addition of 0.36 wt. % diethylenetriamine in inventive treatmentfluid (6) decreased the gel-time to approximately 550 minutes, comparedto approximately 750 minutes in control treatment fluid (2). A furtherincrease in the diethylenetriamine concentration to 1.5 wt. % ininventive treatment fluid (8) decreased the gel-time to about 500minutes. Likewise, as shown in FIG. 3, addition of 0.36 wt. %triethylenetetraamine in inventive treatment fluid (9) decreased thegel-time to approximately 500 minutes, compared to approximately 750minutes in control treatment fluid (2). A further increase in thetriethylenetetraamine concentration to 1.5 wt. % in inventive treatmentfluid (11) decreased the gel-time to approximately 475 minutes. As shownin FIGS. 2 and 3, the two oligomeric polyamines produced comparablegel-time results to one another at like concentration. Further, uponcomparison to FIG. 1, the gel-times produced by the amino alcohols andoligomeric polyamines were comparable to one another at likeconcentration. In summary, the foregoing example shows that the amountof crosslinkable polymer can be decreased through use of a gel-timemodifier comprising at least one amino group.

Example 2 Gel-Times at 160° F. in Gellable Treatment Fluids Comprising at-Butylacrylate/Acrylamide Base Polymer, Polyethyleneimine, and an AminoAlcohol Gel-Time Modifier (Reduction of Base Polymer Amounts)

Control gellable treatment fluids were prepared at the followingcompositions: (12) 350 gal/Mgal “HZ-10” and 30 gal/Mgal “HZ-20” in 2%aqueous KCl base fluid (same as control treatment fluid (2)), and (13)175 gal/Mgal “HZ-10” and 30 gal/Mgal “HZ-20” in 2% aqueous KCl basefluid. Inventive treatment fluids were prepared at the followingcompositions: (14) 175 gal/Mgal “HZ-10,” 30 gal/Mgal “HZ-20,” and 0.36%by weight ethanolamine in 2% aqueous KCl base fluid, and (15) 175gal/Mgal “HZ-10,” 30 gal/Mgal “HZ-20,” and 0.5% by volumetriethanolamine in 2% aqueous KCl base fluid.

The viscosities of the above treatment fluids were measured as afunction of time in order to determine their gel-times. Viscositymeasurements were made at 160° F. FIG. 4 shows an illustrative plot ofviscosity as a function of time at 160° F. for various gellabletreatment fluids comprising a t-butylacrylate/acrylamide base polymer,polyethyleneimine, and, optionally, an amino alcohol gel-time modifier.As shown in FIG. 4, control treatment fluid (12) had a gel-time ofapproximately 750 minutes. When the base polymer concentration washalved in control treatment fluid (13), the gel-time increased toapproximately 1200 minutes. Addition of 0.36 wt. % ethanolamine ininventive treatment fluid (14) produced a gel-time of approximately 950minutes. Addition of 0.5 vol. % triethanolamine in inventive treatmentfluid (15) produced a gel-time of approximately 1100 minutes. Althoughthe gel-times of the inventive treatment fluids did not reach those ofthe original control treatment fluid (12), the gel-times were stillsignificantly reduced compared to that seen for control treatment fluid(13). In the case of inventive treatment fluids (14) and (15), thegel-times were comparable to those obtained when about 215-275 gal/Mgalof base polymer was used in the treatment fluid without the aminoalcohol gel-time modifier being present. In summary, the foregoingexample shows that the amount of base polymer can be decreased throughuse of an amino alcohol gel-time modifier.

Example 3 Gel-Times at 160° F. in Gellable Treatment Fluids Comprising at-Butylacrylate/Acrylamide Base Polymer, Polyethyleneimine, and an AminoAlcohol Gel-Time Modifier (Reduction of Base Polymer and CrosslinkablePolymer Amounts)

A control gellable treatment fluid was prepared at the followingcomposition: (16) 175 gal/Mgal “HZ-10” and 30 gal/Mgal “HZ-20” in 2%aqueous KCl base fluid (same as control treatment fluid (13)). Inventivetreatment fluids were prepared at the following compositions: (17) 175gal/Mgal “HZ-10,” 30 gal/Mgal “HZ-20,” and 0.36% by weight ethanolaminein 2% aqueous KCl base fluid, (18) 175 gal/Mgal “HZ-10,” 30 gal/Mgal“HZ-20,” and 0.75% by weight ethanolamine in 2% aqueous KCl base fluid,and (19) 175 gal/Mgal “HZ-10,” 30 gal/Mgal “HZ-20,” and 1.55% by weightethanolamine in 2% aqueous KCl base fluid.

The viscosities of the above treatment fluids were measured as afunction of time in order to determine their gel-times. Viscositymeasurements were made at 160° F. FIG. 5 shows an illustrative plot ofviscosity as a function of time at 160° F. for various gellabletreatment fluids comprising a t-butylacrylate/acrylamide base polymer,polyethyleneimine, and, optionally, an amino alcohol gel-time modifier.As shown in FIG. 5, control treatment fluid (16) had a gel-time ofapproximately 1300 minutes. When 0.36-0.75 wt. % ethanolamine was addedin inventive treatment fluids (17) and (18), the gel-time decreased toapproximately 1000 minutes. In contrast, when 1.5 wt. % ethanolamine wasused in inventive treatment fluid (19), the gel-time actually increasedto approximately 1400 minutes. Thus, in a treatment fluid comprisingreduced concentrations of both base polymer and crosslinkable polymer,excessively high concentrations of ethanolamine actually served as agel-time retarder, rather than as a gel-time promoter. However, at lowerconcentrations of ethanolamine, lower concentrations of the base polymerand the crosslinkable polymer can be used to obtain a comparablegel-time to that obtainable using higher concentrations of thesecomponents.

Example 4 Gel-Times at 250° F. in Gellable Treatment Fluids Comprising at-Butylacrylate/Acrylamide Base Polymer, Polyethyleneimine, and an AminoAlcohol Gel-Time Modifier

Control gellable treatment fluids were prepared at the followingcompositions: (20) 250 gal/Mgal “HZ-10” and 20 gal/Mgal “HZ-20” in 2%aqueous KCl base fluid, and (21) 167 gal/Mgal “HZ-10” and 20 gal/Mgal“HZ-20” in 2% aqueous KCl base fluid. An inventive treatment fluid wasprepared at the following composition: (22) 167 gal/Mgal “HZ-10,” 20gal/Mgal “HZ-20,” and 1% by volume ethanolamine in 2% aqueous KCl basefluid.

The viscosities of the above treatment fluids were measured as afunction of time in order to determine their gel-times. Viscositymeasurements were made at 250° F. FIG. 6 shows an illustrative plot ofviscosity as a function of time at 250° F. for various gellabletreatment fluids comprising a t-butylacrylate/acrylamide base polymer,polyethyleneimine, and, optionally, an amino alcohol gel-time modifier.As shown in FIG. 6, control treatment fluid (20) had a gel-time ofapproximately 80 minutes. Decreasing the base polymer concentration incontrol treatment fluid (21) lengthened the gel-time to greater than 200minutes. It is also notable the gel strength, as measured by themagnitude of the observed viscosity, was considerably lower in controltreatment fluid (21). Inclusion of ethanolamine in inventive treatmentfluid (22) lowered the gel-time to approximately 120 minutes. Inaddition, the gel strength of inventive treatment fluid (22) wasconsiderably greater than that of control treatment fluid (21). Insummary, the amino alcohol gel-time modifier again produced a reducedgel-time relative to a control treatment fluid lacking the gel-timemodifier.

Example 5 Gel-Times at 160° F. in Gellable Treatment Fluids Comprising at-Butylacrylate/Acrylamide Base Polymer, Polyethyleneimine, an AminoAlcohol Gel-Time Modifier, and a Quaternary Ammonium Salt Gel-TimeModifier

Control gellable treatment fluids were prepared at the followingcompositions: (23) 350 gal/Mgal “HZ-10” and 30 gal/Mgal “HZ-20” in a 2%aqueous KCl base fluid (same as control treatment fluid (2)), and (24)175 gal/Mgal “HZ-10” and 30 gal/Mgal “HZ-20” in a 2% aqueous KCl basefluid (same as control treatment fluid (13)). Inventive treatment fluidswere prepared at the following compositions: (25) 175 gal/Mgal “HZ-10”and 30 gal/Mgal “HZ-20” in 2% aqueous tetramethylammonium chloride, and(26) 175 gal/Mgal “HZ-10” and 30 gal/Mgal “HZ-20” in 2% aqueoustetramethylammonium chloride also comprising 0.5% ethanolamine byweight. The source of tetramethylammonium chloride was “CLAY FIX II”,which is available from Halliburton Energy Services of Duncan, Okla. Itis to be noted in inventive treatment fluids (25) and (26), thetetramethylammonium chloride replaced the KCl as the salt in the basefluid.

The viscosities of the above treatment fluids were measured as afunction of time in order to determine their gel-times. Viscositymeasurements were made at 160° F. FIG. 7 shows an illustrative plot ofviscosity at 160° F. as a function of time for various gellabletreatment fluids comprising a t-butylacrylate/acrylamide base polymer,polyethyleneimine, tetramethylammonium chloride, and, optionally,ethanolamine. As shown in FIG. 7, control treatment fluid (23) had agel-time of approximately 750 minutes. When the base polymerconcentration was halved in control treatment fluid (24), the gel-timeincreased to approximately 1300 minutes. In contrast, when the 2%aqueous KCl base fluid of control treatment (24) was replaced with 2%aqueous tetramethylammonium chloride, the gel-time decreased to about900 minutes in inventive treatment fluid (25). A further decrease ingel-time was realized in inventive treatment fluid (26) uponincorporation of 0.5 wt. % ethanolamine in the base fluid. In the caseof inventive treatment (26), the gel-time was approximately 750 minutes,which is comparable to that of the original control treatment fluid(23). However, inventive treatment (26) achieved this gel-time with onlyhalf the original amount of base polymer.

Example 6 Gel-Times at 160° F. in Gellable Treatment Fluids Comprising aPartially Hydrolyzed Polyacrylamide Base Polymer, Polyethyleneimine andVarious Gel-Time Modifiers

A control gellable treatment fluid was prepared at the followingcomposition: (27) 175 gal/Mgal “FDP-835™” and 30 gal/Mgal “HZ-20™” in a2% aqueous KCl base fluid. Inventive treatment fluids were prepared atthe following compositions: (28) 175 gal/Mgal “FDP-835™,” 30 gal/Mgal“HZ-20 ™” and 0.38% by volume ethanolamine in 2% aqueous KCl base fluid;(29) 175 gal/Mgal “FDP-835™,” 30 gal/Mgal “HZ-20 ™” and 0.5% by volumetriethylenetetraamine in 2% aqueous KCl base fluid; and (30) 175gal/Mgal “FDP-835™,” 30 gal/Mgal “HZ-20 ™” and 0.70% by volumetriethylenetetraamine in 2% aqueous KCl base fluid.

A control gellable treatment fluid was prepared at the followingcomposition: (31) 175 gal/Mgal “FDP-835 ™” and 30 gal/Mgal “HZ-20 ™” ina 7% aqueous KCl base fluid. Inventive treatment fluids were prepared atthe following compositions: (32) 175 gal/Mgal “FDP-835™,” 30 gal/Mgal“HZ-20 ™” and 0.38% by volume ethanolamine in 7% aqueous KCl base fluid;(33) 175 gal/Mgal “FDP-835™,” 30 gal/Mgal “HZ-20 ™” and 0.5% by volumetriethylenetetraamine in 7% aqueous KCl base fluid; and (34) 175gal/Mgal “FDP-835™,” 30 gal/Mgal “HZ-20 ™” and 0.70% by volumetriethylenetetraamine in 7% aqueous KCl base fluid. “FDP-835 ™” is apartially hydrolyzed polyacrylamide having a molecular weight of about640,000 that is available from Halliburton Energy Services of Duncan,Okla. The source of tetramethylammonium chloride was “CLAY FIX II™.”

The viscosities of the above treatment fluids were measured as afunction of time in order to determine their gel-times. Viscositymeasurements were made at 160° F. FIG. 8 shows an illustrative plot ofviscosity at 160° F. as a function of time for various gellabletreatment fluids comprising a partially hydrolyzed polyacrylamide,polyethyleneimine and various gel modifiers in a 2% KCl base fluid. FIG.9 shows an illustrative plot of viscosity at 160° F. as a function oftime for various gellable treatment fluids comprising a partiallyhydrolyzed polyacrylamide, polyethyleneimine and various gel modifiersin a 7% KCl base fluid. The results showed that in a 2% KCl base fluid,the gel-time modifiers increased the gel-times, whereas in 7% KCl thesame concentrations of the gel-time modifiers shortened the gel-times.It should be noted that the gel-times generally can increasesignificantly at higher salt concentrations, primarily due to theanionic character of the partially hydrolyzed polyacrylamide. It isbelieved that the foregoing results demonstrate that the gel-times oftreatment fluids can be advantageously modified using gel-time modifiersin combination with appropriate inorganic salt concentrations.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to one of ordinary skill in the art havingthe benefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered,combined, or modified and all such variations are considered within thescope and spirit of the present invention. While compositions andmethods are described in terms of “comprising,” “containing,” or“including” various components or steps, the compositions and methodscan also “consist essentially of” or “consist of” the various componentsand steps. All numbers and ranges disclosed above may vary by someamount. Whenever a numerical range with a lower limit and an upper limitis disclosed, any number and any included range falling within the rangeis specifically disclosed. In particular, every range of values (of theform, “from about a to about b,” or, equivalently, “from approximately ato b,” or, equivalently, “from approximately a-b”) disclosed herein isto be understood to set forth every number and range encompassed withinthe broader range of values. Also, the terms in the claims have theirplain, ordinary meaning unless otherwise explicitly and clearly definedby the patentee. Moreover, the indefinite articles “a” or “an,” as usedin the claims, are defined herein to mean one or more than one of theelement that it introduces. If there is any conflict in the usages of aword or term in this specification and one or more patent or otherdocuments that may be incorporated herein by reference, the definitionsthat are consistent with this specification should be adopted.

What is claimed is the following:
 1. A gellable treatment fluid comprising: an aqueous base fluid; a base polymer comprising an acrylamide monomer unit; an organic crosslinking agent comprising a crosslinkable polymer selected from the group consisting of polyethyleneimine, polyvinylamine, any derivative thereof, any salt thereof, and any combination thereof; and a gel-time modifier comprising at least one amino group, any salt thereof, any derivative thereof, or any combination thereof; wherein a concentration of the gel-time modifier in the gellable treatment fluid ranges between about 0.1% to about 2% by weight and a ratio of the base polymer to the organic crosslinking agent ranges between about 5:1 to about 50:1.
 2. The gellable treatment fluid of claim 1, wherein the base polymer comprises a polymer selected from the group consisting of a partially hydrolyzed polyacrylamide, a copolymer of acrylamide and t-butyl acrylate, any derivative thereof, and any combination thereof.
 3. The gellable treatment fluid of claim 1, wherein the gel-time modifier comprises at least one compound selected from the group consisting of amino alcohols, oligomeric polyamines, any salt thereof, any derivative thereof, and any combination thereof.
 4. The gellable treatment fluid of claim 3, wherein the gel-time modifier comprises at least one amino alcohol selected from the group consisting of ethanolamine, diethanolamine, triethanolamine, propanolamine, any salt thereof, any derivative thereof, and any combination thereof.
 5. The gellable treatment fluid of claim 3, wherein the gel-time modifier comprises at least one oligomeric polyamine selected from the group consisting of diethylene triamine, triethylene tetraamine, tetraethylene pentaamine, any salt thereof, any derivative thereof, and any combination thereof.
 6. The gellable treatment fluid of claim 3, wherein the gel-time modifier comprises at least one oligomeric polyamine having a molecular weight of less than about
 400. 7. The gellable treatment fluid of claim 1, wherein the gellable treatment fluid further comprises at least one additional gel-time modifier that comprises a quaternary ammonium salt.
 8. The gellable treatment fluid of claim 1, wherein the base polymer comprises a copolymer of acrylamide and t-butyl acrylate, and the gel-time modifier comprises at least one amino alcohol selected from the group consisting of ethanolamine, diethanolamine, triethanolamine, propanolamine, and any combination thereof.
 9. The gellable treatment fluid of claim 8, wherein the gellable treatment fluid further comprises at least one additional gel-time modifier that comprises a quaternary ammonium salt.
 10. The gellable treatment fluid of claim 1, wherein the base polymer comprises a copolymer of acrylamide and t-butyl acrylate, and the gel-time modifier comprises at least one amino alcohol selected from the group consisting of diethylene triamine, triethylene tetraamine, tetraethylene pentaamine, and any combination thereof.
 11. The gellable treatment fluid of claim 10, wherein the gellable treatment fluid further comprises at least one additional gel-time modifier that comprises a quaternary ammonium salt. 